1. Field of Use
The present invention relates to memory systems and more particularly to an apparatus for simplifying the construction and expansion of such systems.
2. Prior Art
It is well known that modular memory systems permit ready expansion of user memory system or memory space. In order to accommodate such expansion, memory system manufacturers have been required to construct a number of different memory systems having different memory capacities or different size increments of memory. This, in turn, has necessitated the construction of a number of different types of memory units.
One prior art system disclosed in U.S. Pat. No. 4,001,790 assigned as named herein employs an arrangement which can utilize the same memory board construction for any one of a number of memory modules which connected, to a memory controller. In the arrangement, one type of memory board (mother board) includes the control logic circuits and another type of memory board (daughter board) contains the memory module. It is required that the memory module be capable of being plugged into any one of a number of different positions.
In this type of arrangement, it is possible to upgrade and expand the capacity of memory system utilizing the two types of memory boards mentioned above. The memory increment or memory size in this case corresponds to the capacity of the daughter board.
To reduce the number of different types of memory boards, the prior art system disclosed in U.S. Pat. No. 4,296,467 employs a number of memory modules identical in layout and construction. Each board includes rotating chip selection circuits which include a set of switches and an arithmetic unit. By altering the set of switches, the arithmetic unit is conditioned to generate a desired logical row address for enabling chips physically positioned at an initial row location in response to different address values.
While the arrangement reduces the number of different types of memory boards to a minimum, the system is required to include address configuration circuits. Such circuits normally contain a further set of switches and comparison logic circuits for generating signals representative of the addressable memory space or memory increment being provided by a particular board. Also, expansion beyond the maximum capacity of the board still requires utilization of different board types.
U.S. Pat. No. 4,303,993, assigned to the same assignee as named herein, discloses a memory subsystem which utilizes memory module boards of identical construction. Each board includes a set of switches which couple to the memory present circuits. By altering the set of switches, the memory present circuits can be conditioned to generate an output signal indicating the same increment of memory or memory module board is present when a different memory segment is being addressed.
Arrangements of the type described above require field or installation personnel to set up the set of switches on each memory board to define the size, segment or memory space which is being added or installed in the system. This tends to complicate the assembly or maintenance procedures, particularly when the memory system can be configured to provide a variety of different addressing ranges. The problem is further complicated where memory boards can be constructed from a variety of different types of memory parts and with different densities of memory chips.
According, it is a primary object of the present invention, to provide a technique and apparatus for constructing a low cost modular memory system.
It is a further object of the present invention to provide a low cost memory system which can be constructed from a variety of different types of memory parts and which provides a variety of different memory densities.